Light control means



Feb. 9, 1932. G. JoBsT 1,843,981

LIGHT CONTROL MEANS Filed Aug. 5. 1927 M ,NvENToR G NTHEK JOBST BY QM(9.44m

ATTORNEY Patented Feb. 9, 1,932

UNITED ysTA'rEsA PATENT OFFICE GNTHER JOBST, F BERLIN, GERMANY,ASSIGNORTO GESELLSCHAFT FUR DRAHTLOSE TELEGRAPHIE M. B. H., OF BERLIN,GERMANY, A CORPORATION OF GERMANY LIGHT CONTROL MEANS Application ledAugust 5, 1927, Serial No. 210,992, and in Germany August 6,'A 1926.

The present invention relates to an arrangement adapted for the controlof light, which may be particularly useful for the purposes of wirelesspicture transmission,

il' television, high-speed telegraphy or the recording of electricoscillations and the like.

The light-control means according to the disclosure of the presentinvention is based upon the physicale'ect of diiuse light dis- ?53persion which arises whenever the light passes through a .transparentmedium containing a body of an almost equal index of refraction, and ifby some external iniuence or another the refractive index of the medium5 or of the transparent body, or both, is altered inside the regionwhere the indices of refraction are almost identical. For in thisparticular region. there occurs a very abrupt change in the intensity ofthe light that has 'FO passed or of the light dift'usely dispersed atthe boundary surface ofthe body located in said'medium. The utilizationof the s aid' effeet for the purpose of light control .for prac- P ticalWork constitutes the subject-matter of d the invention. For furtherexplanation the basic physical process shall be described hereinafter inmore detail. For further facts reference may bephad to an article inAnnan lenA der Physik, fourth series, vol. 78, 1925,

o p. 157 where the diffuse radiation of dielectric spheres isinvestigated and where` it is found that, in the limiting case, thematerial of the spheresand'the ambient medium have nearly equal indices`ot refraction. It must be noted that if a non-planar transparent -bodyis exposed to parallel light, then the distribution of the lightscattered by it, as long as the index of refraction of its mate- -iorial differs from that of its surroundings, de-

pends upon the shape of the body and on all sides, as will becomeapparent from a consideration of the accompanying drawings, wherein:

from a non-planar body 'having an index of refraction diieringmateria/ily from that of its surroundings;

Fig. 2 illustrates a distribution of light where the light is passedthrough a body hav- Fig. 1 illustrates the distribution of light ing anindex of refraction equal to that of its surroundings;

Fig. 3 illustrates the light passage where ihe index of refraction ofthe two bodies difers;

Fig. 4 illustrates the intensity of the light as shown graphically as afunction of 21a (Ni-Na) Fig. 5 shows graphically the intensity as afunction of the wave length of the incident light;

F ig. 6 shows apreferred form of the light refractive indices of thebody material and i the surrounding medium. If both indices are alike,then the distribution of the light will resemble the picture 0r sketchshown in Fig. 2; upon a screen which is placed in the rear of the bodyat right angles to the light rays, the intensity isuniformly distributedsince. optically speaking, the body no longer exists. In the ease ofFig. 1, the distribution upon such a screen would look as shown in Fig.3, in otherwords, since the body absorbs nearly all of the incidentlight by diffuse reflection and refraction, it forms a shadow. Thedistribution upon the screen may not be markedly altered by alterationof the refractive indexes as long as the latter are still widelydiscrepant compared with each other. It is v only in the presence ofnearly complete equality, upon approaching or equalization of therefractive indices, that sudden changes in the intensity upon thescreenin the rear of the sphere will occur. The vintensity does notentirelychange abruptly, equalization of unsteadiness taking place by adiffraction effect.

In case the diifusely dispersing body is a glass sphere in a solutionpossessing nearly the same refractive index as the ball, then theintensity law for passing/light, in first approximation is:

if the share of intensity per unit of area of the ball is =1, and if athe diameter of the ball, A the wave-length of incident light, Z theintensity per unit of area of the screen, Na the index of refraction ofthe outer material. Ni the index of refraction of the material and p isa constant whose value depends upon the intensity of the light sourceand the transparency of the light valve. Then from the dependence ofintensity Z upon the wavelength it is possible to tell at once that adiffraction phenomenon is concerned. In Figs. 4 and 5, intensity Z isshown graphically in one case as a function of Q1rc1.(Ni-Na) and in theothercase as a function of A.

The formula is only a first approximation and is only valid as long asZ 1. It will; be seen therefrom that the change of Z responds verystrongly to alterations of the refractive index; when the ball has adiameter of about 1 cm. and if the light of a sodiumilame is used, weget:

dZ d(Ni-Na) of the order of =2 X 101. The intensity upon the screen isvery largely dependent upon changes in the refractive index. Y

If the difference in refractive indices 0r else the wave-length of thepenetrating light is influenced by external agencies of an electrical,magnetic, mechanical, thermal or chemical nature, this makes it possibleto vary the intensity of the light falling upon the screen. -As stated,this effect inside the boundary region where the indices of refractionare equal to each other, is of extremely great sensitiveness. Forinstance, if we take into consideration the case of electric control(for it is this case that plays the most important part in the practiceof picture transmission and television), the arrangement oflight-control relays (light valves) can be chosen in the followingmanner according to this invention (Fig. 6)

Suppose a vessel G is filled with a liquid and that inside the vesselthere is a transparent ball K whose trefractive index is approximatelythe same `vas the refractive index of the liquid that is employed.Suppose the ball and the liquid are' disposed between two electrodes Eland E2 to which the electrical potentials are supplied. The light from aluminous source S is made parallel by optical means, such as a lens L,so that the rays pass through between the electrode plates and fall uponthe screen M. Now, according to the invention, the material of thetransparent sphere is so selected, and such a substance is chosen forthe liquid, that their refractive indices are nearly the same. Then thecontrol potential is supplie-d to the electrodes, and the variations inintensity can be observed upon the screen. The arrangement can be sochosen that, when uniniuenced, there is brightness while darkening isproduced under the influence of potentials. Of course, the controlscheme could also be reversed; in other words, there may be normaldarkness while brightness is produced by action of the potential. Oneadvantage of the arrangementas hereinbefore disclosed over known lightcontrol schemes is that it is possible to operate with unpolarizedlight, so that all such losses as are occasioned in the polarizer andthe analyzer, are dispensed with and avoided. To be sure, there is aselective action for one direction of polarization for the alteration ofthe refractive index by the electric field, so that, under certaincircumstances, it may seem more suitable to use a polarizer. But it mayalso be possible to dispose two light valve arrangements in series,according to the spirit of the present invention, -as shown by Fig. 8,and to iniuence the two by means-of fields at right angles to, orcrossing, each other. 'Then the luminous variations which are polarizedat right angles to the first field, will be preferentially influenced bythe second field. And in this case an analyzer can be omitted. Thesensitivity of the arrangement may be still further enhanced by thatseveral transparent bodies are disposed in a row inside the liquid. Mostsuitable is an arrangement in which the liquid consists of nitrobenzoland the transparent body of a glass sphere of ahnost identical indicesof refraction. As regards the potentials that are to-be applied, it maybe a good plan in the case of various liquids whose insulation powersare not ideal, to protect the equipment against the chances of wrongpolarity for this often is conducive to breakdown. For this purpose,rectified A. C. potentials are preferab used for .the control, that is,for instance, in the manner that the potential is taken off across theterminals of a resistance R which is inserted in the plate circuit of ansimplifying rectifier D, the alternating potentials in this scheme beingfed to the grid of the tube through transformer T or equiva lentconnected with an appropriate input circuit. It is also possible to usea biasing potential and to superpose the control potential upon thelatter. The use of a biasing potential is recommendable also for thereason to insure proportional light control with favorable and highsensitivity. It goes without saying that as to detail, the constructionsmay be quite different and diversified.

In addition to what has been stated above, it may be further mentionedthat the body of different nature which is employed in the lightpermeable medium need not necessarily be a body of a chemically orphysically different nature; indeed for so far as the optical effect isconcerned it is entirely sufiicient if p art of the transparent medium,by some convenient external influences, is kept under other physicalconditions than the ambient, in other words, a certain part of atransparent liquid, for instance. may be exposed to the action of aconcentrated electrical or magnetic field, with the result that thisparticular part will then possess, optically speaking, differentproperties than the part of the medium uninfluenced by such field, andit will thus act as a body possessing a different nature. Hence, theglass sphere can be replaced by a bounded or separated region of thenitrobenzol which is subject to electrical potentials. A

Having thus described my invention T claim:

1. A light control system comprising, a light source, a transparentmedium in the path of the light rays issuing from vsaid source, atransparent body having at least one surface crossing the optical axisin other than a plane normal thereto arranged within said medium andcontiguous therewith, said body having different chemical and 'physicalproperties from said medium and an index of refraction approximately thesame as said medium, and means for applying an electric field to saidcontained body for producing internal refraction within said system soas to abruptly change the intensity of the penetrating light inaccordance with the application of said electric field.

2. A light control system comprising, a.. light source, a transparentmedium in the path of the rays issuing from said source, a body havingat least one optically effective surface crossing the optical axis inother than that internal refraction will occur o n the applicationo suchfield.

4. A light valve comprising a containel` filled with a solution ofnitrobenzol and a spherical body contained therein and having an indexof refraction'substantially equal to the index of refraction of saidnitrobenzol under normal conditions, and means for applying anelectricfield to said nitrobenzol and said body. whereby the index ofrefraction of said body is changed an internal refraction occurs Withinthe system so as to control the emitted'light in accordance with theelectric field applied.

5. A light control system comprising a, light source, a transparentmedium inthe path of the light rays issuing from said source, atransparent body having at least one surface crossing the optical axisin other than a plane normal thereto'arranged inside said medium andcontiguous therewith, said body and medium having substantially equalindices of. refraction under normal conditions, and means for applyingan external force on said light control system for producing a change inthe value of said indices of refraction relative to each other forproducing variations in the intensity of the penetrating light. l

GNTHER J OBST.

the plane normal thereto and having a sim- .i

ilar index of refraction to said medium contained within said medium,said body having different chemical and physical properties from saidmedium, a light sensitive material in the path of the light rayspenetrating said medium, and means for applying a potential to said bodyfor producing abrupt change-s in the intensity of said penetratinglight.

3. A light valve comprising two contiguous bodies normally having likeindices of re.- fraction, one of said bodies being arranged along theoptical axis of said light valve and having at least one surfacecrossing the optical axis in other than a plane normal thereto andadapted to change its index of refraction on .the application of anelectric field. and the surface of contiguity being so shaped

